Automatic tuning arrangement



Patented Oct. 3, 1939 UNITED STATES PATENT OFFICE Nelson P.

Hazeltine Corporation, ware Case, Great Neck, N. Y., assignor to a corporation of Dela- Application October 22, 1937, Serial No. 170,318

9 Claims.

This invention relates to automatic tuning arrangements for carrier-wave signal-receiving apparatus and, while of general application, it is particularly suitable for tuning wave signal receivers utilizing automatic amplification control. In many'installations of carrier-wave signalreceiving apparatus, it is desirable to incorporate a motor driven tuning arrangement as a part of the apparatus. Mechanical systems for remote tuning are, in general, unsatisfactory because oi! the mechanical'complexity oi the apparatus linking the tuning units of the receiver with the control device. This is particularly true of remote tuning arrangements such as required for automobile receivers. For this reason, a motor driven control has been used extensively comprising a push-button controlled electrical motor or equivalent device for operating the tuning unit of the receiver. When such a motor is used, a satisfac- 20 tory speed of tuning between stations is generally i found to be very much too fast for accurate tuning in the vicinity of the desired station, resulting in an over-running of the station. On the other hand, if a slow speed motor is used, it is generally unsatisfactory because of the time required to tune between stations which are widely separated on the dial of the receiver.-

It is an object of the invention, therefore, to provide an automatic tuning control apparatus for speedily and accurately tuning a carrierwave signal-receiving device.

It is another object of the invention to provide a motor operated tuning control for tuning a radio receiver which operates at a relatively high speed between stations but at a relatively low speed in the vicinity of stations having a relatively great signal strength.

In accordance with the invention, 'a carrierwave receiving apparatus having automatic amplification control is provided with a motor for driving the tuning unit of the receiver and means for remotely controlling the motor for either direction of rotation. Means are provided for varying the speed of the motor in accordance with the amplitude of the received signal. This means is preferably dependent upon the direct current component of the space current of one or more tubes of the receiver which are subjected to automatic amplification control. Thus, when the receiver is being tuned in the vicinity of a station having a relatively strong signal, the direct space current of the tubes subject to automatic amplification control is less and the speed of the motor is correspondingly reduced. In one embodiment of the invention, means are provided dependent upon the speed-reducing means for the tuning motor, for muting the receiver during a portion of the tuning operation.

The novel features which are believed to be characteristic of this invention are set forth with 5 particularity in the appended claims. The invention itself, however, both as to its organization and operation, together with other objects and advantages thereof, will best be understood by reference to the following specification taken 10 in connection with the accompanying drawing, in which Figs. 1 and 2 are circuit diagrams, partially schematic, of a radio broadcast receiver incorporating the invention in somewhat different forms. e 15 Referring more particularly to Fig. 1 of the drawing, there is illustrated one form of the tuning arrangment embodied in a radio receiver of the well-known superheterodyne type. Briefly described, the receiver comprises a radio-fre- 20 quency amplifier and selector ill of one or more stages, connected to an antenna-ground circuit II and coupled to a frequency-changing unit or oscillator-modulator I2. The radio-frequency amplifier I0 may be of any conventional type and includes one or more tunable selector circuits, each provided with an adjustable tuning condenser l3, and one or more vacuum tubes l4. Similarly, the frequency-changing unit i2 may be of any conventional radio-frequency selector circuit and its local oscillator circuit adjustable tuning condensers, represented generally by condenser IS. A modulator tube I6 is included in frequency-changing unit l2. Connected in cascade to the output circuit of the frequency-changing unit l2 are an intermediate-frequency amplifier ll of one or more stages, a detector and automatic amplification control-bias supply 19, an audio-frequency amplifier 2| of one or more stages, and a sound reproducer 22. The bias potential derived from the automatic amplification control s'ource i9 may be applied to the tubes of one or more of the stages of the radio-frequency amplifier ill, the

modulator tube I 8, and to the tubes of one or more of the various stages of the intermediatefrequency amplifier I! by way of conductor 20.

It will be understood that only the direct current circuits and elements in the space discharge paths of tubes l4, l6, and I8, which are necessary to describe the present invention, are shown in the diagram and that the alternatingcurrent circuits of these tubes may be of a conventional design which is well understood in the art.

Considering, first, the operation of the receiver type and includes in its 30 as a whole, without regard to the details of the tuning arrangement of the invention, per se, a desired received signal wave is selected and arnplified in the radio-frequency amplifier lid and is converted into a modulated intermediate-frequency signal by the frequency changer l 2. The signal as thus converted is further amplified in amplifier il and rectified by the detector l9, thereby deriving the audio frequencies of modulation which are, in turn, amplified in the audioirequency amplifier 2i and reproduced-in the sound reproducer 22. The amplification of. the received signal is subject to automatic control by the control-bias potential derived from the source it according to the manner well understood in the art.

Referring now more particularly to the details of the tuning arrangement of the invention, there is provided an alternating current motor M having a series field 23, the motor 1V5 being mechanically coupled to and preferably positioned adjacent the tuning condensers i3 and iii. The motor is driven from a source or" supply 241 and remotely controlled through a control station indicated generally at 25. The control station may be positioned at a convenient location on the receiver cabinet or at a point remote from the receiver and comprises two normally open doublecontact push-button switches F and R to provide, respectively, for forward and reverse rotation of the motor. The switches F and R are connected as ordinary reversing switches for the series field 23 of the motor M and are mechanically interlocked by means of the bar 26 to prevent simul= taneous operation of both switches.

There is provided a saturable reactor 271 having an iron core 28 of three legs, two alternating current windings 29 and 3b, which are connected in series with each other and the motor M, and

a direct current Winding 33 disposed on the middle leg of the iron core 28 and shunted by a condenser 32. The direct space current oi the tubes 54, It, and i8 is supplied from a suitable source of direct current, such as battery 3i. Windlngs 29 and 30 are so poled that alternating currents in these windings induce potentials of opposite polarity in the winding 33.

In considering the operation oithe tuning arrangement described above, it will be seen that the tuning units l3 and i5 can be controlled in either direction by means of the reversible motor M from the remote control station 25 by operation of one or the push buttons F or R for the desired direction of rotation. Thus, if the push button F is operated to close its contacts, the field 23 is connected in series with motor M and windings 29 and 30 across 'thesupply source 245. If the push button R is operated, the field 23 is connected with opposite polarity in series with windings 29 and 30 and the armature of motor M across the supply source 24. However, direct space currents of tubes l4, l6, and it vary widely with variations in the automatic amplification control bias applied to the tubes. Thus, when the receiver is tuned to a strong signal, the bias applied to the tubes is such that direct current of relatively small values fiows through the! winding 33 from the source of supply 3 I. At this time iron core 28 is not saturated, and the reactive drop across the windings 29 and 30 results in a relatively small voltage being applied to the motor M, so that it rotates relatively slowly. If the receiver is tuned to a station having a weak signal strength, the direct current in the winding 33 is correspondingly increased, saturating the awasee core 28 and thereby reducing the reactance of the windings 29 and 3b and increasing the motor speed. Thm, it will be seen that the circuit of Fig. 1 provides an arrangement whereby the tuning condensers it and it can be operated in either direction to tune toward a desired station on the dial. The tuning operation is relatively rapid between stations, but as a station of appreciable signal strength is approached, the

speed of the motor M decreases so that it is rela tively easy to stop the motor quickly by releasing the button F or R to tune the receiver accurately to the desired signal. An auxiliary switch it may be provided, if desired, for the purpose of short-circuiting the windings iii and 3% when it is desired to tune to a station at a remote point on the dial, thus to prevent the normal operation of the invention to slow the speed of the motor at each of the intervening stations of strong signal strength.

Another embodiment of the invention is disclosed in Fig. 2 and is. very similar in its operation to that or" the circuit of Fig. 1. Corresponding parts of the two systems have been given the same reference numerals. The system of Fig. 2 differs from that of Fig. l primarily in the fact that a resistor (it is inserted in series with the motor M when it is desired to reduce its speed, in lieu of the saturable reactor 21 of Fig. l. The motor M of Fig. 2 may be suitable for operation on either alternating or direct currents. In this embodiment of the invention, a relay, having a coil 35 connected in series with the space current paths of tubes ill, l6, and i8, is provided with contacts 36 for inserting'the resistor 35' in the motor circuit. A second normally open set of contacts 3i is provided on the relay and conh ated in the audio-frequency channel of the receiver in such manner that, when closed, loudspeaker 22 is silenced. The relay 35-36-37 is preferably so designed that there is a small differential between the value 01 its pick-up and drop-out current,-so that the relay operates to change the speed of the motor at approximately the same point whether the receiver is being tuned away from or toward a desired strong signal.

In considerating the operation of the circuit of Fig. 2, it will be seen that the contacts 36 and 3? of the relay open when the receiver is being tuned in the vicinity of a signal having an appreciable signal strength. When the winding 35 is enerizecl, the contacts 36 short-circuit the resistor 34! in the motor circuit to increase its speed. Simultaneously, the contacts 37 mute the audio-frequency amplifier 2! for silent tuning. It is believed that, with the description given above in. connection with Fig. 1, the operation of the circuit of Fig. 2 will be readily apparent and that no further description thereof is necessary.

While there have been described what are at present considered to be the preferred embodiments of thisinvention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A carrier-wave signal receiver comprising a stage of amplification subject to automatic amplification control, a tuning unit, a motor for operating said tuning unit, manual control means for said motor, and means for changing the speed of speed ll 6. A carrier-wave signal receiver comprising a s,174,see

operation of said timing unit to a low but appreciable speed in response ceiver through a signal of a predetermined amplitude comprising means for controlling the speed of operation of said tuning unit in accordance with the magnitude of the bias or said amplification control.

2.1 carrier-wave signal receiver comprising a timing unit, a motor for operating said tuning unit,manual control means for said motor, means for developing an automatic volume control bias,

and means for changing t e speed of operation of said tuning unit to a low but'appreciable speed in to the tuning of said receiver through a signal of predetermined amplitude comprising means resp n ve to said bias for controlling the speed otoperation of said tuning unit in accordance with the magnitude of said bias.

3. A carrier-wave signal receiver comprising a stage of amplification comprising a vacuum tube,- means for automatically controlling the amplification ot-said tube, a tuning unit, a motor for operating said tuning unit, manual control means for said motor, and means for changing the speed of operation of said tuning unit to a lowbut appreciable speed in respense to the tuning oi the receiver through amplitude comprising means for controlling the speed of operation of said tuning unit in accordance with the average space current of said tube.

4. A carrier-wave signal receiver comprising a stage of amplification subject to automatic amplification contrql,' a tuning unit, a motor for operating 'said tuning unit, manual directional control means for said motor, means for changing the speed of said motor toja low but appreciable in response to the tuning o! the receiver through a signal of predetermined amplitude comprising an impedance in circuit with said motor, and meanstor controlling said impedance in accordance with the magnitude of the bias of said amplification control.

5. A carrier-wave signal receiver comprising a stage of amplification subject to automatic amplification control. a tuning unit, an alternating current motor for operating said tuning unit,

manual control means for said motor, means for changing the speed of said motor to a low but appreciable speed in response to the tuning of the receiver through a signal of predetermined amplitude comprising a saturable reactor in circuit with said motor, and means for controlling the saturation or said reactor in accordance with the magnitude of said amplification control.

to the tuning of the rea signal of predetermined stageof amplification subjectto automatic amplification control, a tuning unit, a motor for operating said tuning unit, manualdirectional control means ior said motor, means for changing the speed speed in response to the tuning of the receiver through a signal of predetermined amplitude comprising an impedance in said motor circuit, and means comprising a relay operated in accordance with the magnitude of said amplification control for short-circuiting said impedance, thereby to vary the speed of said motor.

7. A carrier-wave stage of amplification subject to automatic amplification control, a tuning unit, a motor for operating said tuning unit, manual directional control means for said motor, means for changing the speed of said motor to a low but appreciable speed in response to the tuning of the receiver through a signal above a predetermined amplitude comprising an impedance in circuit with said motor, means for controlling said impedance in accordance with the magnitude of said amplification control, and means comprising said meansfor controlling said impedance for muting said receiver.

8. A carrier-wave signal receiver comprising a stage of amplification subject to automatic amplification control, a tuning unit, a motor for operating said tuning unit, manual directional .control means for said motor, means for changing the speed oi said motor to a low butappreciable speed in response to the tuning of the receiver through a signal of predetermined amplitude comprising an impedance in circuit with said motor, means comprising a relay operable in accordance with the magnitude of said amplification control for short-circuiting. said impedance, thereby to vary the speed of said motor, and

means comprising said relay for muting said receiver.

9. A carrier-wave tuning unit, a motor for operating said tuning unit, manual control means for said motor, means for developing an automatic bias control, means for utilizing said bias control to control the amor said motor to a low but appreciable signal receiver comprising a signal receiver comprising a plification in said receiver, and means for changing the speed of operation of said tuning unit to a predetermined low fixed speed in response to the tuning of the receiver through a signal oi greater than a predetermined amplitude comprising means responsive to said bias for controlling the speed of operation oi said tuning unit in accordance with the magnitude of said bias.

mason 2. case. 

